1. Field of the Invention
The present invention relates in general to a chemical mechanical polishing (CMP) apparatus. In particular, the present invention relates to a washer for the CMP apparatus.
2. Description of the Related Art
A process commonly used in fabrication of integrated circuits to create a planar topography is chemical mechanical polishing (CMP) process. This process involves chemically removing a surface while also mechanically grinding or polishing it. The combined action of surface chemical reaction and mechanical polishing allows for a controlled, layer by layer removal of a desired material from the wafer surface, resulting in a preferential removal of protruding surface topography and a planarized wafer surface.
However, if the CMP process is out of control, the wafer""s surface becomes non-uniform. For an etching process, if contact windows or via holes are formed on a substrate with a non-uniform level, the endpoint of the etching process is not easy to maintain. Some contact windows or via holes may be overetched; some contact windows or via holes may not reach the predetermined depth and thereby experience open circuits. For a lithography process, the accuracy of the exposure is easily lost. With the increase of integration, elements are shrunk and it is important to smooth the substrate surface to a uniform level.
FIG. 1 schematically illustrates a conventional CMP apparatus 100 with a platen 110, a dresser 120, a wafer carrier 150, and a washer 160.
Referring to FIG. 2, a polishing pad 112 of polyester is positioned on the platen 110, and a slurry is positioned on the polishing pad 112. The wafer carrier 150 includes a guide ring 152, a top ring 154 and a backing ring 156. The top ring 154 is supported on the backing ring 156. The guide ring 152 is positioned on the outer periphery of the top ring 154 to surround wafer 102 so that the wafer 102 is not disengaged from the wafer carrier 150. The wafer is polished while being pressed between the wafer carrier 150 and the platen 110.
After polishing, the polishing pad 112 is washed by the dresser 120. However, some residue, from the reactant of the slurry and the removed surface layer, still remains on the polishing pad 112. If the residue is not removed, it can damage the resulting polished wafer.
FIG. 3 shows the top view of the CMP apparatus. After removing the wafer 102 from the platen 110 by the wafer carrier 150, the dresser 120 is moved on the platen 110 and the polishing pad 112 is cleaned by clockwise or counterclockwise action of the dresser 120. The residue in the polishing pad 112 is scraped by the dresser 120 every one or several turns of the CMP process. The dresser 120 is then washed by immersion in the washer 160 filled with water to remove the residue attached to a bottom disk 125 of the dresser 120. The dresser 120 rotates in the washer 160 to make water flow. The flowing water removes the residue.
However, using the flowing water to remove all of the residue is difficult. Conventionally, the bottom disk 125 is frequently changed by shutting down the CMP apparatus, to prevent the residue from damaging the wafers.
The present invention provides a CMP apparatus comprising a platen, a wafer carrier, a washer with a cleaning device, and a dresser. A polishing pad is disposed on the platen. The wafer carrier holds a wafer on the polishing pad, and the wafer carrier can move on to and off of the polishing pad. The dresser has a bottom disk contacting the polishing pad, and can move between the polishing pad and the washer. A diamond zone disposed on the bottom disk can clean the polishing pad, and the cleaning device can clean the diamond zone.
The cleaning device can be at least one scrubber disposed in the lower part of the washer, or an ultrasonic device, or combination thereof.